1. Field of the Invention
This invention relates generally to impact resilient assemblies, and more particularly to impact resistant assemblies having a resilient head and a substantially inflexible shank.
2. Description of the Prior Art
In bowling alleys, the construction of backstops at the end of each alley serves to absorb the impact of the bowling balls once they strike the bowling pins, or otherwise pass the end of the alley on which the pins are positioned. The backstop also serves to deflect the balls in the desired direction to fascilitate ball retrieval, which is generally accomplished by the use of automated ball retrieval equipment. The speed and mass of the balls and the repeated impact shocks to which the backstops are subjected dictate that the backstops be constructed of rugged, impact resistant materials and components. For this reason, prior art backstops have been constructed of layers of oak board, hard rubber and a softer foam rubber, with the less resilient layer being positioned at the rearmost portion of the backboard, thereby absorbing these impacts with successive layers of increased rigidity to minimize shock damage and to dissipate the blows' shocks. A canvas or similar tear resistant material is placed on top of the outermost foam layer to minimize tearing of the foam.
Such prior art backstops are provided with a plurality of spaced apart resilient rivets, which are placed through holes running the width of the backstop in order to further reduce and dissipate these impacts. Such prior art rivets comprise unitary elongated rubber members which are provided with an enlarged head on one end and a tapered portion on the other end, which is provided with an enlarged circumferential rib. These rivets are inserted through the corresponding hole in the backstop and the tapered end is pulled to stretch the rivet's elongated shaft, thereby firmly seating the enlarged head against the front face of the backstop. The shaft is further stretched until the circumferential rib is pulled out of the hole at the rear face of the backstop. Tension on the tapered end is then relaxed, and the rib is allowed to rest against this rear face. The tension of the stretched shaft then continues to force the head against the front face and the rib against the back face of the backboard.
However, the stretching of the rubber shaft causes stress facturing and hence a weakening of the thermoplastic material. Under such high tension, the repeated, severe impacts of the bowling balls thereon causes premature failure of these prior art rivets, and they must therefore be replaced frequently, which is a costly and time consuming operation.
A variety of fastening devices have been developed by the arts for a large number of end uses. These are represented by the following patents. However, none is readily adapted to solve the above problems in construction of highly reliable and long-lived bowling alley backstops which serve the purposes of minimizing and distributing the above-discussed impact shocks as a result of direct impact thereon of the weighty bowling balls.
U.S. Pat. No. 121,060 relates to a bolt in which the head of the bolt is contiguous to a rectangular portion and in which the shaft is of a circular cross-section and is provided with flanges to prevent the turning of the bolt when used in wood. The shaft's rectangular portion is said to prevent the turning of the bolt when it is used in iron. The end portion of the shaft is screw-threaded to receive a screw-nut.
U.S. Pat. No. 2,432,986 relates to a non-conductive fastener including a metal core and a plastic shell. The metal core is serrated along its entire length to enhance bonding of the plastic shell.
U.S. Pat. No. 2,935,552 also relates to a non-conductive fastener but employs a plastic body and a metallic core of triangular shape which is provided with peripherally located lug members which assist in physically gripping the plastic body into which the core is to be driven.
U.S. Pat. No. 2,993,950 discloses a multicomponent self-tapping and non-conductive fastener including a metal core, a synthetic resin shell and a metallic tapping screw insert.
U.S. Pat. No. 3,457,823 relates to a protective bolt and nut assembly utilizing an insulating cover formed of plastic to protect the nut and bolt assembly from shocks from structural members.
U.S. Pat. No. 3,557,654 discloses a composite fastener having a plastic head molded onto a metal insert having a threaded shank. Annular weathertight seals are provided to lock the plastic head in the appropriate position.
U.S. Pat. No. 3,592,100 discloses an insulating screw with a threaded shank and an enlarged head coated with a plastic insulating material.
U.S. Pat. No. 4,295,767 relates to corrosion resistant fasteners having a carbon steel treaded shank with a die cast zinc or aluminum head, and employing a reformable plastic washer positioned within the head. The annular recess defined between the head and a portion of the cylindrical shank receives a washer or seal which is reformable, which seal completely fills the recess about the shank of the fastener and provides the seal against corrosion.
U.S. Pat. No. 4,373,842 discloses a plastic-headed fastener comprising a plastic member that fits over the head of the fastener, an annular seal and a metallic screw shank. The annular seal is deformable and is fabricated from plastic.